This invention relates generally to the field of colorimetry and more particularly to an improved two-beam colorimeter.
Two-beam colorimeters are used for the colorimetric determination of a liquid component. They include an interference filter, the function of which is to filter only a specific band width out of a wide-band light produced by a light source. Also included is a reference filter, arranged in the path of a comparison beam, the function of which is, on the one hand, to compensate for the light absorption brought about by the measuring cuvette or vessel in which the sample or object liquid is contained, and on the other hand, to bring the photo-resistors, which may differ in their characteristics, to a common measurement level.
It has been determined that the reference filter, by itself, is not adequate to produce precise colorimetric measurement. For example, the cuvette is generally supplied by liquid by means of suitable conduits which interconnect the cuvette with another liquid container. Vapors can pass through the conduits into the cuvette, thereby causing the cuvette windows or the entire vessel to easily become cloudy. This, of course, can result in a mismeasurement.
A further shortcoming of known two-beam colorimeters lies in the fact that when the colorimeter is in continuous operation, the intensity of the light source diminishes, e.g., due to the vaporization of the filament. It is known that this deficiency can be alleviated by regulating the operating voltage of the light source, but circuitry suitable for this purpose is relatively expensive.
To provide a two-beam colorimeter which can operate relatively service-free as a module for an automatic analysis device, and which constantly produces accurate measurement values, and to otherwise improve upon and further develop two-beam colorimeters are objects of the present invention.